This invention relates to a tomographic X-ray apparatus for the production of transverse layer images of an exposed object, consisting of a patient's support, an X-ray measuring arrangement with an X-ray source, which generates a bundle of X-rays penetrating the exposed object and of which the cross sectional extent perpendicular to the plane of the layer is equal to the thickness of the layer, for example, and a radiation receiver which ascertains the radiation intensity beyond the object by scanning the projected bundle of rays, and a driving device for the measuring arrangement including a pivot mounting for accommodating rotational movements of the X-ray measuring arrangement, the apparatus further including a measurand converter for the conversion of the signal supplied by the radiation receiver into a tomographic image.
For detecting the layer image, the rotational movements may take place through equidistant angular amounts, each in alternating sequence with a displacement of the measuring arrangement along a straight line perpendicular to the central ray of the bundle of X-rays, when a single detector is used as the radiation receiver. Alternatively, it is possible to dispense with the displacements along a straight line path if the radiation receiver is built up of a multiplicity of ray detectors whose signals are simultaneously processed by the measurand converter. For example, the X-ray beam may be fan-shaped and the detectors may be arranged in succession so as to simultaneously receive the X-ray energy after traverse of paths of equal length.
A tomographic X-ray apparatus of this kind is described in U.S. Pat. No. 3,974,388 issued Aug. 10, 1976. The exact positioning of a patient and the accurate choice of the transverse layer to be imaged is difficult, because it is difficult to ascertain the exact transverse layer of the body which is being scanned by the X-ray energy. The cited patent represents a tomographic apparatus seeking to facilitate the desired exact positioning of the patient wherein markings are applied relative to a precisely determined patient location such as the eye-ear line. In this apparatus, for example, an adhesive band may be adhered to the side of the patient's head, having a scale disposed longitudinally of the patient which is utilized in conjunction with a light visor to enable a precise determination of the position of the scanning layer relative to the reference line.